[llvm] [ValueTracking] Propagate sign information out of loop (PR #175590)

[Kshitij Paranjape via llvm-commits]

kshitijvp wrote:

```
  for (unsigned I = 0; I != 3; ++I) {
    if (auto *Operation = dyn_cast<InstTy>(PN->getIncomingValue(I));
        Operation) {
      Value *Op0 = Operation->getOperand(0);
      Value *Op1 = Operation->getOperand(1);
      Value *Op2 = Operation->getOperand(2);

```

These lines must be causing the failure.
Because PHINode has only 2 incoming values
thus accessing PN->getIncomingValue(2) will cause
crash.

https://github.com/llvm/llvm-project/pull/175590